Nicobar Fan provenance evolution - A fingerprint using zircon Hf isotopes
Abstract
The India-Eurasia collision juxtapositioned several tectonic blocks with a large spread of accretionary ages. The erosion and runoff on these areas are carried mainly by two river systems, the Indus in the west and the Ganges-Brahmaputra in the east. The Ganges-Brahmaputra rivers feed the Bengal-Nicobar Fan, the world largest active deep-sea fan. Recent IODP Expedition 362 - The Sumatra Subduction Zone - recovered a sedimentary section at the Nicobar Fan turbidites that comprises Early Miocene to Holocene strata. These cores allowed us to access the sedimentary record of the India-Eurasia collision. The recognition of the different source areas for Ganges-Brahmaputra rivers and consequently for Nicobar Fan is a challenging task because U-Pb signature shows overlaps of populations. However, same uniqueness based mainly in first cycle zircons (<400 Ma) Hf isotopes can be used to distinguish these overlaps. Therefore, we performed zircon U-Pb-Hf isotopes in 17 samples of deep-sea sandy and silty turbidites of the Nicobar Fan and analyzed all zircon grains younger than 450 Ma by Hf isotopes. Our results indicate a significative reorganization in first cycle zircons. At the late Miocene, there was an increase in zircon grains sourced from the Bomi-Chayu and Lohit Batholiths (Himalaya Syntaxis) compared to the previously dominant Gangdese rocks (Lhasa Block). Meanwhile, after the Miocene-Pliocene boundary, a significant increase (more than twice) in the first cycle zircons is observed. The Pliocene-Pleistocene interval also shows enrichment in zircon with ages between 10 - 30 Ma, with Hf signature related to Higher and Lesser Himalaya Leucogranites. Our study using zircon U-Pb-Hf isotopes shows that since the late Cenozoic, the Nicobar Fan records a significant change in the sediment routing system and the zircon Hf isotopes is a powerful tool for distinguishing zircon populations overlaps.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T13F0257G
- Keywords:
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- 8110 Continental tectonics: general;
- TECTONOPHYSICS;
- 8122 Dynamics: gravity and tectonics;
- TECTONOPHYSICS;
- 8169 Sedimentary basin processes;
- TECTONOPHYSICS;
- 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS